The Characterization of β Adrenoceptor Subtypes in the Rat Amygdala and Hippocampus

(-)-[125I]Iodocyanopindolol ((-)ICYP), is a ligand with high specific activity and nearly equal affinity for β1, and β2, adrenoceptors in a variety of tissues. Unfortunately, (-)ICYP also has affinity for 5HT1B serotonin receptors. To get an accurate estimate of β adrenoceptors in the rat amygdala and hippocampus, (-)ICYP binding studies were done with membranes from these limbic structures in the presence of 10μM serotonin to prevent the binding of (-)ICYP to serotonin receptors. Under these conditions, (-)ICYP binding to amygdaloid and hippocampus membrane preparations is saturable and reversible. Scatchard analyses revealed in both regions a single class of binding sites with an equilibrium dissociation constant (KD) of 18.5 pM for the amygdala and 19.6 pM for the hippocampus. The hippocampus has a significantly lower density of binding sites (Bmax) than amygdala (51.6 vs 62.3 fmol/mg membrane protein, p